"tony sayer" wrote ...
Yes they do, in fact we've got a broadcast transmitter site which is
fed
by a bit of BT, (British Telecom, the national Telco), overhead wire
for some miles and no hum at all!.

The telecom people would find it very amusing to see how
much their customers take for granted. They work very hard
and use many tricks and techniques to keep power-mains hum
out of phone loops. Apparently they are doing a good job if
we think that it is effortless.